connetion: fixing None timeout issue

Connection objects set timeout to a default value in case a timeout is
not specified. However, Target defaults timeout to None and passes that
to connection, overridng the default.

This commit ensures that default timeout remains set if calling code
specified timemout as None.

Fix for issue

https://github.com/ARM-software/devlib/issues/34

devlib/utils/android.py

@@ -152,6 +152,7 @@ class AdbConnection(object):
     # maintains the count of parallel active connections to a device, so that
     # adb disconnect is not invoked untill all connections are closed
     active_connections = defaultdict(int)
+    default_timeout = 10
 
     @property
     def name(self):
@@ -168,8 +169,8 @@ class AdbConnection(object):
         else:
             raise DevlibError("Unknown line ending")
 
-    def __init__(self, device=None, timeout=10):
-        self.timeout = timeout
+    def __init__(self, device=None, timeout=None):
+        self.timeout = timeout if timeout is not None else self.default_timeout
         if device is None:
             device = adb_get_device(timeout=timeout)
         self.device = device

devlib/utils/ssh.py

@@ -127,6 +127,7 @@ class SshConnection(object):
 
     default_password_prompt = '[sudo] password'
     max_cancel_attempts = 5
+    default_timeout=10
 
     @property
     def name(self):
@@ -138,7 +139,7 @@ class SshConnection(object):
                  password=None,
                  keyfile=None,
                  port=None,
-                 timeout=10,
+                 timeout=None,
                  telnet=False,
                  password_prompt=None,
                  ):
@@ -150,6 +151,7 @@ class SshConnection(object):
         self.lock = threading.Lock()
         self.password_prompt = password_prompt if password_prompt is not None else self.default_password_prompt
         logger.debug('Logging in {}@{}'.format(username, host))
+        timeout = timeout if timeout is not None else self.default_timeout
         self.conn = ssh_get_shell(host, username, password, self.keyfile, port, timeout, telnet)
 
     def push(self, source, dest, timeout=30):